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Seasonal variation of ozone deposition to a tropical rain forest in southwest Amazonia

机译：亚马逊西南部热带雨林中臭氧沉积的季节性变化

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Within the project EUropean Studies on Trace gases and Atmospheric CHemistry as acontribution to Large-scale Biosphere-atmosphere experiment in Amazonia(LBA-EUSTACH), we performed tower-based eddy covariance measurements ofO3 flux above an Amazonian primary rain forest at the end of the wetand dry season. Ozone deposition revealed distinct seasonal differences inthe magnitude and diel variation. In the wet season, the rain forest was aneffective O3 sink with a mean daytime (midday) maximum depositionvelocity of 2.3 cm s−1, and a corresponding O3 flux of−11 nmol m−2 s−1. At the end of the dry season, the ozonemixing ratio was about four times higher (up to maximum values of 80 ppb)than in the wet season, as a consequence of strong regional biomass burningactivity. However, the typical maximum daytime deposition flux was verysimilar to the wet season. This results from a strong limitation of daytimeO3 deposition due to reduced plant stomatal aperture as a response tolarge values of the specific humidity deficit. As a result, the averagemidday deposition velocity in the dry burning season was only 0.5 cm s−1. The large diel ozone variation caused large canopy storageeffects that masked the true diel variation of ozone deposition mechanismsin the measured eddy covariance flux, and for which corrections had to bemade. In general, stomatal aperture was sufficient to explain the largestpart of daytime ozone deposition. However, during nighttime, chemicalreaction with nitrogen monoxide (NO) was found to contribute substantiallyto the O3 sink in the rain forest canopy. Further contributions werefrom non-stomatal plant uptake and other processes that could not be clearlyidentified.Measurements, made simultaneously on a 22 years old cattle pasture enabledthe spatially and temporally direct comparison of O3 dry depositionvalues from this site with typical vegetation cover of deforested land insouthwest Amazonia to the results from the primary rain forest. The meanozone deposition to the pasture was found to be systematically lower thanthat to the forest by 30% in the wet and 18% in the dry season.
机译：在项目 EU ropean S 关于 T 种族气体和 A 大气层 CH 的研究中作为对 A mazonia（LBA-EUSTACH）中 L 大尺度 B 大气-大气实验的贡献，我们进行了基于塔的涡动协方差旱季结束时亚马逊热带雨林上空的O 3 通量测量臭氧沉积显示出幅度和迪尔变化的明显季节性差异。在雨季，雨林是有效的O 3 汇，平均日（中午）最大沉积速度为2.3 cm s -1 ，相应的O -11 nmol m -2 s -1 的3 通量。在干旱季节结束时，由于强烈的区域生物质燃烧活性，臭氧混合比约为潮湿季节的四倍（最高为80 ppb）。但是，典型的日间最大沉积通量与雨季非常相似。这是由于白天的O 3 沉积受到严重限制的缘故，这是由于植物气孔孔径减小，这是对较大的特定湿度不足值的响应。结果，干烧季节的平均午间沉积速度仅为0.5 cm s -1 。较大的diel臭氧变化引起较大的冠层存储效应，从而掩盖了所测涡流协方差通量中臭氧沉积机理的真实diel变化，对此必须进行校正。通常，气孔孔径足以解释白天臭氧沉积的最大部分。然而，在夜间，发现与一氧化氮（NO）的化学反应对雨林冠层的O 3 汇有很大贡献。 在22岁的牛牧场上同时进行的测量能够对O 3 进行时空直接比较，这进一步促进了非气孔植物的吸收和其他无法明确识别的过程。从该地点的干沉降值，到亚马逊西南地区森林被砍伐的土地的典型植被覆盖到原始雨林的结果。结果发现，在牧场中，杂草区的沉积物系统性地比湿地中的沉积物系统地低，在湿润季节比森林中低30％，而在干燥季节则低18％。

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